[Test] Add debug names to unnamed test disposables

- This helps to track down disposables which are never disposed, and
  reduces confusion when printing disposables in general (the names will
  now be meaningful, instead of endless lists of "newDisposable" and
  "TestDisposable").

^KT-64099

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/AbstractInBlockModificationTest.kt

@@ -139,7 +139,7 @@ private fun doTestInBlockModification(
  * @return **true** if out-of-block happens
  */
 private fun LLFirDeclarationModificationService.modifyElement(element: PsiElement): Boolean {
-    val disposable = Disposer.newDisposable()
+    val disposable = Disposer.newDisposable("${LLFirDeclarationModificationService::class.simpleName}.disposable")
     var isOutOfBlock = false
     try {
         project.analysisMessageBus.connect(disposable).subscribe(